Long time diver.. new (one year) nitrox diver. Redlining your O2 SAT then switching to air? Wouldn't 21% still give you a O2 loading at depth? Greatly reduced but if you where truly at the redline then switched to air you'd still go over, right? I think this would be REAL dangerous if diving with a computer and then switched to AIR instead of 21% then the O2 would not be tracked.. or am I just all wet in this conclusion?